In railroad locomotive operations, the throttle, dynamic brake and reverser actions of the locomotive, locomotives or other drive units, are controlled by the operator or engineer in the cab of the lead unit by manipulating three handles extending from the control stand, one handle each for throttle, dynamic brake, and reverser. The throttle handle, of course, controls the development of the tractive effort of the locomotive; i.e., the diesel engines or other power units. The dynamic brake handle controls the development of a retarding force known a dynamic brake, for example the electric motors driving the locomotive wheels, to place them in either motor mode where they will drive the wheels, or in generator mode, where they will function as a retarding force. The reverser handle controls the forward and reverse rotation of the electric motors to selectively drive the train forward or rearward, and includes a neutral position. Pursuant to current practice, the control stand is designed to be a man-to-machine interface and ideally is strictly an electronic/electric device having no direct mechanical, hydraulic or pneumatic connections the devices controlled. Instead, encoding means are preferably provided within the control stand to read and interpret the positions of the three handles, and convey appropriate signals, indicative of such positions, to an associated microcomputer. The associated microcomputer is programmed to interpret the encoded signals regarding the positions of the throttle, dynamic brake and reverser handles, as positioned at the control stand, and then electronically issue corresponding commands to manipulate the devices intended within the locomotive or locomotives. When utilizing a microcomputer, the throttle, dynamic brake and reverser commands effected at the control stand, are dependent upon the given angular positions of the three control handles, which are normally sensed and monitored by rotary encoding devices, which are mechanically coupled to associated rotary axles to which the control handles are secured, utilizing cams to actuate microswitches or contacts to provide a signal to the microcomputer as noted above. Such mechanical devices leave a lot to be desired, in that they do not provide the exacting degree of handle position determination as desired, are prone to mechanical failure, are cumbersome, space consuming, and require frequent adjustment.
There has been considerable development effort in the recent past to improve the encoder technology, particularly with regard to obtaining a more absolute determination and reading of the control handle positions. With regard to the throttle and dynamic brake controls in particular, there is need for more accurate and absolute encoder determinations because these controls can be set over a rather wide range of setting. The reverser control, on the other hand, is positionable to only three positions, namely, a "neutral" position at the center, and "forward" and "reverse" positions at either end. Accordingly, with regard to the reverser control, there is no need for any costly and complicated encoder technique to determine an absolute and exacting control handle position or command, as all that is necessary to determine in which of the three positions the handle is located, namely, "forward", "reverse" or "neutral". Accordingly, while the prior art mechanically linked encoders leave much to be desired, the newer absolute position encoders are more costly and complicated than is necessary for the simple task of encoding the three positions of the reverser control handle.